This invention relates to a bath and process for plating a gold or gold alloy deposit. More particularly, it relates to such a sulfite complex and nitrogen-free diphosphonic compound.
The use of alkali gold sulfite electroplating baths has been disclosed in U.S. Pat. Nos. 3,057,789; 3,475,292; and 3,666,640, the contents of which are incorporated herein by reference. An improvement over the processes described in the foregoing patents is provided by the present invention wherein a nitrogen-free phosphonic compound is added to the plating bath in order to enhance the stability of the bath and improve the brightness and grain refinement of the gold electrodeposit. The use of both nitrogen-containing and nitrogen-free phosphonate compounds has been suggested in gold plating baths where the gold is present in the form of potassium gold cyanide. (See U.S. Pat. No. 3,762,969.)